Dr. Drew:
I am speculating here but if Greener's ever had a British damascus 'Rosetta Stone' it may have been disposed of when the Greener firearms collection was sold off to America in the 1960s. (See English author/photographer David Grant's recent feature article in The DGJ on "Greener's Oldest New Gun" for more details.)
However, the Greener records do list the type of barrels and barrel steels used on their guns per the respective serial # -- so if a Greener owner can get those details from the firm and photograph the gun, a photo archive of at least Greener barrel types and descriptions could be developed example by example. (I will ask Dryhurst (again) when we speak.)